There's a lot of reasons for NOT weaning before 6 months, head control, choking, digestive maturity and potential for allergic reactions are just some of them.
The latter is not true. There is some emerging (albeit inconclusive) evidence that "early" weaning (i.e. weaning between 17 and 26 weeks) reduces risks of allergies later in life. The only downside is the risk of minor diarrhoea. I remember reading lots of underlying research and making an informed decision to wean DD at 17 weeks. She is now 17 months and is a brilliant eater.
...waiting longer is no problem, food before 1 is for fun.
Sorry but this statement is plain wrong. According to WHO (page 22):
www.who.int/nutrition/publications/guiding_principles_compfeeding_breastfed.pdf
However, breast milk is relatively low in several minerals such as iron and zinc, even after accounting for bioavailability. At 9-11 months of age, for example, the proportion of the Recommended Nutrient Intake that needs to be supplied by complementary foods is 97% for iron, 86% for zinc, 81% for phosphorus, 76% for magnesium, 73% for sodium and 72% for calcium (Dewey, 2001).
Also, a recent study in Australia has shown a significant percentage of babies and toddlers are not getting sufficient iron (which is vital for cognitive development). I personally think the "food before one..." slogan has got something to do with it. It is not a statement you will hear from experienced health care professionals but, unfortunately, it gets overused in internet forums and in baby groups:
www.ncbi.nlm.nih.gov/pubmed/26571345
Our results showed that 32·6 % of infants and 18·6 % of toddlers had inadequate Fe intake.